WOODY SPECIES DIVERSITY AND CARBON STOCK IN COFFEE-BASED HOMEGARDEN AGROFORESTRY IN DELLOMENNA DISTRICT Of BALE ZONE, SOUTHEASTERN ETHIOPIA

Abstract

Agroforestry is accompanies different diversity of plants and has a unique capacity of balancing the net carbon emissions as a sink and reservoir for carbon dioxide at both above and belowground. The objective of this study was to investigate woody species diversity and carbon stock in coffee-based homegarden agroforestry in the Dellomenna District of Bale Zone, Ethiopia. Three study kebeles (Wabaro, Erba and, Chiri) were selected purposively. In each selected kebele, two sites were identified and selected randomly. Within sites systematic sampling techniques were employed to select the homegardens and laid down plots. Hence, forty-eight sample plots each having an area of 10 *10 m was laid for trees and shrubs with a height of >1.5 m and DBH >2.5cm.Within major plots five subplots of 2*2 m, at four corners and in the center, were laid for seedling /saplings having height > 0.50 m and less than 1.5 m or with D40 cm or DBH <2.5 cm including the seedlings with a height of <0.50 m. Therefore, the diameter and heights were measured by using diameter tape and hypsometer respectively. Trees, saplings and seedlings encountered in the plots were recorded and identified using the standard procedure. Soil samples from four corners and at the center were taken by pressing an auger to a depth of 30 cm. Hence, 48 composite soil samples were used for organic carbon determination. Undisturbed soil bulk density was collected by using a 6.2 cm length and 5 cm diameter core sampler for this purpose 48 soil samples were used. AGB of individual trees and coffee was estimated using allometric equation of AGB (tree) = 0.091 * d2.472 and AGB (coffee) = 0.147*d240 cm respectively. Then means exhibited significance difference was tested by LSD at p<0.05 using Genstat18th edition (software). The diversity of woody species was analyzed by using diversity indices. A total of 39 woody species representing 24 families were recorded. Out of the total woody species encountered in the 48 quadrats, 71.9 % were trees and shrubs, 28.1 % was seedlings and saplings. Shannon diversity and evenness at kebele level were ranged from 1.68 - 2.5 and 0.64 - 0.79 respectively. The mean Shannon diversity and evenness at plot level and structural parameters show significant variation at p<0.05. Almost 96.07% of the variation of the carbon stock of woody species in coffee based homegarden agroforestry was due to diameter variation and the remaining 3.93% variation was due to other unexplained factors. The overall mean of each carbon pool in the coffee based homegarden agroforestry was 48.63,9.73 and, 111.2ton ha 1for AGBC, BGBC and, SOC respectively.The total mean carbon stock for biomass and SOC stock were 175.1 and 333.5 ton per hectare respectively. Generally the study indicates that coffee-based homegarden agroforestry could be one option to combat the problems of climate change through reducing the carbon emission. However, coffee-based homegarden agroforestry of the area is dominated by a fruit trees and this result in low species diversity decline in the frequency of some indigenous woody species, leading to a loss in carbon stock and species diversity